This application is based on and claims priority to Japanese Patent Application No. 2000-163383, filed May 31, 2000, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to a four-cycle engine for a marine drive, and more particularly to a four-cycle engine that includes a variable valve timing mechanism.
2. Description of Related Art
A typical outboard motor comprises a power head and a housing unit depending from the power head. The power head includes an internal combustion engine that drives a marine propulsion device such as a propeller through a driveshaft and a propulsion shaft both journaled on the housing unit. The marine propulsion device is attached to the end of the housing unit and is in a submerged position during operation.
Four-cycle internal combustion engines tend to have advantageous emission control and high performance relative to two-cycle internal combustion engines. Accordingly, it is becoming popular for marine drives such as outboard motors to employ such four-cycle internal combustion engines. Typically, the four-cycle engine has intake and exhaust ports, both of which communicate with a combustion chamber. One or more camshafts are often provided to actuate the intake and exhaust valves between an open position and a closed position at proper timing so that air is introduced into the combustion chamber and exhaust gases are discharged therefrom. Automobile engines often include a variable valve timing mechanism that can advantageously change the opening and closing timing of the valves depending on certain operating conditions, such as engine speed. The valve timing usually is advanced at high engine speeds to ensure high charging efficiency and high performance. Valve timing usually is delayed at low engine speeds to ensure high combustion efficiency, fuel economy and good emission control.
Typically, the variable valve timing mechanism is driven by hydraulic pressure. Often the hydraulic pressure is supplied by an existing lubricant oil pump that circulates lubricant oil through the engine. Typically, oil that has been pressurized by the oil pump is directed into one of two pathways. One pathway leads to the engine body to lubricate components of the engine; another pathway leads to an oil control valve and a variable valve timing (VVT) mechanism. The oil control valve controls the delivery of oil to the VVT mechanism in order to control the mechanism. A problem arises because the relatively long passage from the lubricant oil pump to the oil control valve results in delayed responsiveness. Thus, the hydraulic pressure to the VVT mechanism cannot be adequately stabilized and performance of the VVT mechanism suffers.
A need therefore exists for an improved four-cycle engine for a marine drive having a variable valve timing mechanism that has improved responsiveness and improved hydraulic stability.
In accordance with one aspect, the present invention includes a four-cycle engine comprising an engine body, at least one cylinder, a piston reciprocatingly arranged in the cylinder, and a cylinder head assembly. A combustion chamber is defined between the cylinder head assembly, cylinder and piston. A port opens into the combustion chamber, and a valve selectively opens and closes the port. A camshaft has a cam configured to actuate the valve. A variable valve timing mechanism is configured to vary the valve timing of the valve by varying an angular position of the camshaft. A fluid pump is adapted to provide fluid under pressure to a control valve. The control valve is configured to selectively supply fluid to the variable valve timing mechanism so as to control the angular position of the camshaft. An engine lubrication system has an oil reservoir and an oil pump. The oil pump draws oil from the oil reservoir.
In accordance with another aspect of the invention, a four-cycle engine comprises an engine body defining at least one cylinder having a piston arranged to reciprocate therein, and a cylinder head attached to the engine body. A combustion chamber is defined between the cylinder, piston and cylinder head. A port opens into the combustion chamber, and a valve mechanism is configured to selectively open and close the port. A camshaft having a cam lobe is configured to actuate the valve mechanism. A variable valve timing mechanism cooperates with the camshaft, and is configured to selectively vary the angular position of the camshaft in response to hydraulic fluid inputs supplied by a driving system. The driving system comprises a hydraulic fluid pump and a control valve. A lubrication system is configured to supply lubricant oil to the engine body. The lubrication system comprises an oil pump and an oil reservoir.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.